regulator: minor cleanup of virtual consumer

Minor cleanup to the regulator set_mode sysfs support:
switch to sysfs_streq() in set_mode(), which is also
a code shrink.  Use the same strings that get_mode()
uses, shrinking data too.

Signed-off-by: David Brownell <dbrownell@users.sourceforge.net>
Acked-by: Mark Brown <broonie@opensource.wolfsonmicro.com>
Signed-off-by: Liam Girdwood <lrg@slimlogic.co.uk>